[ObjC ARC] Converts ios/chrome/browser/ui/reader_mode:reader_mode to ARC.

ios/chrome/browser/ui/reader_mode/reader_mode_infobar_delegate.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/ui/reader_mode/reader_mode_infobar_delegate.h"
 
 #include "base/strings/utf_string_conversions.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 ReaderModeInfoBarDelegate::ReaderModeInfoBarDelegate(
     const base::Closure& callback)
     : callback_(callback) {}
 
 ReaderModeInfoBarDelegate::~ReaderModeInfoBarDelegate() {}
 
 infobars::InfoBarDelegate::InfoBarIdentifier
 ReaderModeInfoBarDelegate::GetIdentifier() const {
   return READER_MODE_INFOBAR_DELEGATE_IOS;
 }
 
 base::string16 ReaderModeInfoBarDelegate::GetMessageText() const {
   // TODO(noyau): Waiting for text to put here.
   return base::ASCIIToUTF16("Open in reader mode");
 }
 
 bool ReaderModeInfoBarDelegate::Accept() {
   callback_.Run();
   return true;
 }